Orthogonal Frequency Division Modulation (OFDM) requires sub-carrier frequencies that are orthogonal to each other such that cross-talk between sub-channels is eliminated. While this greatly simplifies the design of the transmitter and receiver by eliminating the need for filters for each sub-channel, it requires a high degree of frequency synchronization.
OFDM can be extended to an Orthogonal Frequency Division Multiple Access (OFDMA) system by assigning different OFDM sub-channels to different users. However, the frequency synchronization requirement and communication requirements for the sub-channel assignment make the system less ideal for large numbers of users. An advantage of the system described below is that it has fewer communication requirements over previously described OFDMA systems.